Powder charge, Volume vs. weight

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kmw1954

New member
I was just working on a ladder load for a 223 and thought I had enough powder to complete what I was doing but ended up short of finishing with that Lot.

Move on and open a new jar, not a problem.

As I was working this as a control I was weigh checking every drop to stay within a node. But after opening and dropping a load to restart I found my density must have changed.

The target load I had and being measured on an electronic scale was 23.76gr and it was holding consistently until the hopper got very low. After changing Lots and running thru some settling drops the new lot was dropping at 23.94gr.. So here I had the same volume of powder but the weight changed.

At this point I didn't change the measure throw to regain the set point weight I just poured of a little powder from each and then trickled up to the target weight. As at this point in the session I only had 14 more rounds to load.

I also took these last 14 and marked them to indicate the change in powder and measure.

So as the volume did not change I am assuming that the powder density changed. I understand this is common among different Lots and that density can also change in the same powder over time due to humidity changes.

Question is how much does the density need to change before there is a measurable or noticeable effect? Which would play a bigger part, keeping the weight the same or keeping the volume the same? Or does that depend on the powder?
 
It depends on the chemistry of each lot. I would start over working up a load with the new lot if you like that method.

I never changed charge weights across all lots of powder for each cartridge's bullets.
 
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Just for future reference when you start a new lot of powder make a note of the VMD (Volume Measured Density) of the lot. When you run out repeat on the next lot.

Next you may want to give this a read. They point out the powder manufacturers allow a tolerance of 16%.

I also found reference to the 16% tolerance in Lee VMD Data.

So what you are seeing comes as no surprise to me.

How much can the VMD change for you to notice it? Depends on the powder but if you crunch numbers the charge change is not all that much.

Ron
 
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What is the difference between VMD and regular old density?

There is no regular old density that I know of and I am getting pretty old. :)

From the WiKi:
"The density (more precisely, the volumetric mass density; also known as specific mass), of a substance is its mass per unit volume. The symbol most often used for density is ρ (the lower case Greek letter rho), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume"

Lead has more density than water but a pound of lead (7,000 grains) and a pound of water (7,000 grains) weigh the same. They merely occupy different amounts of volume. :)

Ron
 
Reloadron, thanks for the help and time. I understand what you are telling me an do agree though I still feel I am not explaining my thoughts clearly or correctly.

Let me try it this way also. A long while ago I had been loading a powder with a lee Auto Disk measure and got to a point that with one disk I could get three different loads out of the three cavities and they were consistent over a few different sessions, Yes I would see the odd variation in dropped charges but they were always within 0.1gr and with these pistol loads 0.1gr didn't make any significant difference in how they shot. So I never worried about it. I had those loads written down in my log as to the powder and the weight from each of these cavities so I could go back to them.

Then I hadn't loaded any of those for a number of months and the powder sat, closed in the original container. Next time I went to load those I did a check weight and they all were lighter than previously measured. to the point the low charge fell below the start level.

I still loaded the middle load even though it was lighter than previous and when shot I could not discern any significant change.

In this load I am currently working on it is in a 223 bolt rifle and am trying to refine/define a node. It has already proven that a change of .1gr makes a large difference in the repeated accuracy in this load.

In this load an increase from 23.6 to 23.7 makes a large difference and the groups tighten up. An additional .1gr to 23.8 makes no significant change. Yet another additional .1gr to 23.9gr and there is again a large drop off and the groups again open up. So even though the change of just .1gr in minuscule there is a profound effect on the accuracy of the round in this gun.

So once again the question which has a more pronounced effect on a load when all else are equal. A change in weight with the same volume or a change in volume with the same weight?
 
If you have density in the bastardized grain/cc unit, then VMD is just it's reciprocal (the numerator and denominator swapped). If you use them as multipliers, multiplying a volume by density gives you weight, and multiplying a weight by VMD gives you volume. In the Lee dispensing system, which is in cc's of volume, when you know what charge weight you want to dispense, you multiply it by a powder's VMD to see how many cc's to set your Lee measure to, or to pick your scoop or disc insert to have. The drawback is that powder densities vary from lot-to-lot, with some types varying by a spread of as much as 12%. So, I think the wise thing to do is measure the VMD of the lot you have before using it to predict drop weight.
 
I knew a competition shooter who bought a case of powder at a time to last the year without having to tweak his load for changes in density.
I just get a keg of pistol powder and consider myself well off.

I have seen a little difference in density but never anything approaching the 12-16% mentioned above. Good grief that would be 3/4 of a grain on a 5 grain pistol load.
 
Jim

The 12% to 16% being mentioned is not a percentage of load weight but rather the variance powder manufacturers hold to in VMD (Volume Metered Density), that number.

All smokeless powders have a nominal VMD. Volume * Density = Volume. Just as an example the nominal VMD for IMR 4895 is 0.0728. To calculate the volume of a charge it becomes charge weight (grains) * powder VMD = Volume in cc. We can see where the allowable tolerance for VMD has little effect. Just remember it's not about a percentage of charge weight but rather a percentage of the powder volume measured density from a nominal value.

This is frequently called a bastardized formula because if we look up the definition of density it amounts to Density = Mass / Volume and we use a tailored version for smokeless powder.

Ron
 
kmw1954 said:
Reloadron, thanks for the help and time. I understand what you are telling me an do agree though I still feel I am not explaining my thoughts clearly or correctly.

Let me try it this way also. A long while ago I had been loading a powder with a lee Auto Disk measure and got to a point that with one disk I could get three different loads out of the three cavities and they were consistent over a few different sessions, Yes I would see the odd variation in dropped charges but they were always within 0.1gr and with these pistol loads 0.1gr didn't make any significant difference in how they shot. So I never worried about it. I had those loads written down in my log as to the powder and the weight from each of these cavities so I could go back to them.

Then I hadn't loaded any of those for a number of months and the powder sat, closed in the original container. Next time I went to load those I did a check weight and they all were lighter than previously measured. to the point the low charge fell below the start level.

I still loaded the middle load even though it was lighter than previous and when shot I could not discern any significant change.

In this load I am currently working on it is in a 223 bolt rifle and am trying to refine/define a node. It has already proven that a change of .1gr makes a large difference in the repeated accuracy in this load.

In this load an increase from 23.6 to 23.7 makes a large difference and the groups tighten up. An additional .1gr to 23.8 makes no significant change. Yet another additional .1gr to 23.9gr and there is again a large drop off and the groups again open up. So even though the change of just .1gr in minuscule there is a profound effect on the accuracy of the round in this gun.

So once again the question which has a more pronounced effect on a load when all else are equal. A change in weight with the same volume or a change in volume with the same weight?
Click to expand...
I don’t know about anyone else’s definition of a node, but a spread of only .2gr before a major change in accuracy is not an accuracy node.
 
Western Powders Ramshot pages are still up. They list variation for Accurate powders ranging from ±2.2% to ±5.6. The latter is were I got 12% as a ballpark limit.
 
So by all means please inform us of your definition of a node.

I have only been doing this for about 3 months so I may not be as sophisticated as you! So sorry if my node definition offended you.
 
Sorry if I came off as snotty, definitely not meant as such. In rifles I load in .5gr increments and usually find nodes that will span two increments that with fine tuning leads me to a charge that can vary by +- .5 gr, this gives a more than generous leeway for powder measure variances. Once again my deepest apologies for an unintended attitude.
 
Maybe just a little but it's all good.

With this 223 I have been loading in I guess would be 4gr increments such as 22.0, 22.3, 22.6 and so on. With also not having a chrono to measure speed with I have to rely purely on group sizing.

In this case I had found that that at 23.7 the groups shrunk measurable. That was also the last loading I had made. So after getting back home and to the bench I loaded up 18 ea of 23.7, 23.8 and 23.9.gr.. between the 23.7 and 23.8 I could overlay the sample targets, (4 of them) and the could not tell one from the other. That would be a total of 36 shots on 4 targets. The last load, the 23.9gr had moved up and right and already showed signs of opening up. So by my way of thinking and from talking with a number of competition shooters the 23.7 - 23.8gr would indicate a node.
 
The difference you describe is not a lot. Was the new jar a different lot or just a new jar? I guess a better question would be could the difference be not the powder but rather throwing a charge from an almost empty hopper and a full hopper? 0.18 grains is not much of a difference.

You have wisely segregated the rounds from the new jar. If it were me, I wouldn't rework the load unless there is a measurable difference in velocity, ES and/or point of impact.
 
The 12% to 16% being mentioned is not a percentage of load weight but rather the variance powder manufacturers hold to in VMD (Volume Metered Density), that number.

All smokeless powders have a nominal VMD. Volume * Density = Volume. Just as an example the nominal VMD for IMR 4895 is 0.0728. To calculate the volume of a charge it becomes charge weight (grains) * powder VMD = Volume in cc. We can see where the allowable tolerance for VMD has little effect. Just remember it's not about a percentage of charge weight but rather a percentage of the powder volume measured density from a nominal value.

This is frequently called a bastardized formula because if we look up the definition of density it amounts to Density = Mass / Volume and we use a tailored version for smokeless powder.
Click to expand...

Lessee, now, multiply 0.0728 by 47, a common .30-06 M1 load of IMR 4895, you get 3.42 which would conveniently indicate a 3.4 cc dipper.

Now, let us say the VMD is 12% low, 0.0641 meaning the powder is MORE dense; and you use that 3.4 dipper. 3.4/0.0641 = 53.1 grains, which is a substantial overload.
And wait, 53 = 47 + 12.7%. Pretty close within rounding error.
So a change in density will yield the same percentage change in volumetrically measured powder charge.

I never heard of VMD before Lee devised it for easy selection of their fixed charged dippers and discs.
Although if you put it in consistent units, you have specific volume, which I had heard mentioned in school but seldom had use for at work.

I once tried calculating the VMD of a powder on hand and came out nowhere near the Lee number. Probably because my measure technique was not theirs, but it is still not a method I would rely on.
 
For me a node this narrow means weighing each and every round by loading low and trickling up. Which is fine if that’s what you want to do. I prefer to find nodes more forgiving, and then I just set my scale to the proper weight, throw a charge and dump it in the pan. If it varies by more than +- .2gr I dump it back in the hopper and do it again. This way I’m still getting relatively accurate powder amounts well within the larger node but not wasting time trickling up. I feel with this method I get very good consistent accurate loads while still loading in a time efficient manner. If all I get are narrow nodes I try a different powder until I find one with a wider node and start over again.
 
Howland, you are correct the difference in powder charge is not very large But the difference in group size at 100yds is the difference of 1.5" group to a .75" group on the paper. In my mind that is significant.

To answer your question it was a new jar and a different lot# Also because these are test loads each one is dropped into a scale and weighted before being poured into the case. The result is to find if a charge of 23.70 be the target weight would a drop from the measure at 23.85 move out of the zone that I already know that 23.8 is acceptable.
 
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